Method and Apparatus of Beam Training for MIMO Operation and Multiple Antenna Beamforming Operation

ABSTRACT

The disclosed invention provides an efficient method for MIMO beam training for multiple antennas to enable spatial multiplexing MIMO operation and spatial combining in a wireless network. The invention discloses a simple and efficient beam-training algorithm and protocol for MIMO operation that operates in high SNR condition for reliable MIMO operation. In one novel aspect, the best MIMO beam combinations are determined after TX sector sweeping and RX sector sweeping. The best MIMO beam combinations are determined in such a way that no any selected TX/RX sectors come from the same TX/RX antenna/beamformer. The selection criteria includes not only signal quality, but also considers mutual interference and leakage among multiple MIMO spatial streams to improve overall MIMO performance. Simultaneous RX or TX training are also supported to reduce training time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation, and claims priority under 35 U.S.C.§120 from nonprovisional U.S. patent application Ser. No. 14/709,426,entitled “Method and Apparatus of Beam Training for MIMO Operation andMultiple Antenna Beamforming Operation,” filed on May 11, 2015, thesubject matter of which is incorporated herein by reference. ApplicationSer. No. 14/709,426, in turn, is a continuation-in-part of, and claimspriority under 35 U.S.C. §120 from nonprovisional U.S. patentapplication Ser. No. 13/899,540, entitled “Method and Apparatus of BeamTraining for MIMO Operation,” filed on May 21, 2013, the subject matterof which is incorporated herein by reference. Application Ser. No.13/899,540, in turn, claims priority under 35 U.S.C. §119 from U.S.Provisional Application No. 61/650,220, entitled “Method and Apparatusfor Beam Training for MIMO Operation,” filed on May 22, 2012, thesubject matter of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless networkcommunications, and, more particularly, to beam training methods formultiple-input multiple-output (MIMO) operation and for multiple antennabeamforming operation.

BACKGROUND

Spatial multiplexing multiple input and multiple output (MIMO) techniqueis used to increase the data rate (and spectral efficiency) bytransmitting multiple data streams via different spatial pathssimultaneously. Spatial combining technique, on the other hand, refersto the technique that combines the same data stream via differentspatial paths to enhance signal quality. Spatial multiplexing andspatial combining techniques have been widely employed in mobilecommunications systems such as IEEE 802.11n (2.4 GHz and 5 GHz) and IEEE802.11ac (5 GHz). For 802.11n and 802.11ac, the signal wavelength islarge comparing to the feature size of objects in the propagationenvironment. As a result, NLOS signal propagation is dominated by thesignal scattering from various objects. Due to the severe scattering,OFDM signal is often used in such systems and the spatial multiplexingand spatial combining are done on a per-tone (per-subcarrier) basis inthe digital domain.

For higher frequency systems such as IEEE 802.11ad (60 GHz), the signalpropagation characteristics change as the signal wavelength becomessmall comparing to the feature size of objects in the propagationenvironment. As a result, signal propagation is dominated by ray-likepropagation with discrete paths in space. The signal quality can begreatly enhanced if either TX or RX antenna beams or both TX and RXantenna beams are directed toward strong spatial signal path. Theimproved signal quality via aligning the antenna beams with strongspatial signal path manifests both increased signal strength (highersignal-to-noise ratio) and reduced delay spread. Since the delay spreadis reduced, spatial combining can be wholly or partially done in RFdomain (instead of digital domain) to simplify implementation.

In general, phased-array antenna with steerable antenna beam in MIMOoperation provides antenna gain and enables mobility. Eigen-beamformingis one method of antenna beam training. The Eigen-beamforming requirestransmitter and receiver to estimate the channel response matrix first.The channel response matrix is then decomposed using singular valuedecomposition (SVD). The MIMO operation uses n dominant Eigen modes(corresponding to n spatial paths) for transmitting n spatial streams.The Eigen beamforming method suffers from the problem that the channelresponse matrix is obtained in lower signal-to-noise condition since nobeamforming is used during the channel estimation. Additionally, Eigenbeamforming is generally performed in frequency domain employing OFDMsignal.

Another method of antenna beam training is multi-stage iterativetraining using power method. In the power method, the receiver sendsback the normalized receive vector in the n antennas to the transmitter.The transmitter uses the receive vector as the next transmit antennaweight. The antenna weight quickly converges to the first Eigen vectorafter a few iterations. This process continues until the n vectors(antenna weight vectors) are obtained. The power method suffers from theproblem that it only works (converges) in the presence of highsignal-to-noise ratio.

The beam training protocol provided in IEEE 802.11ad involves eithertransmitter or receiver to sweep through a number of antenna beamdirections to determine the beam with the best signal quality. Forefficient beam training, multiple stages of beam training are provided.The initial stage, called the SLS (sector level sweep), provides coarseantenna beam training. The subsequent stage, called the beam refinementprotocol or beam tracking, provides the fine-tuning of antenna beam forimproved pointing accuracy and higher signal quality. These beamtraining protocols are generally used to train a single spatial beam forthe transmission of a single data stream.

A solution is sought for training multiple antenna beam combinations toallow for multiple data streams for increased data rate, or to allowcombining of the same data stream for enhanced signal quality.

SUMMARY

The disclosed invention provides an efficient method for beam trainingto enable spatial multiplexing MIMO operation and spatial combining in awireless network. The invention discloses a simple and efficientbeam-training algorithm and protocol for MIMO operation that operates inhigh SNR condition for reliable MIMO operation without the drawbacks ofprior art methods.

In a first embodiment, an initiator and a responder exchangebeam-training parameters to start a MIMO training procedure. During TXsector sweeping, the initiator sends training packets through all TXsectors, while the responder receives the training packets withomni-direction beam. The responder sends back a set of selected TXsectors with good received signal quality and the corresponding channelmeasurements. During RX sector sweeping, the initiator sends trainingpacket with omni-direction beam, while the responder receives thetraining packets through all RX sectors. The responder determines a setof selected RX sectors with good received signal quality. During beamcombination training, the initiator and the responder sweep through theselected TX sectors and RX sectors together. The responder determinesthe best MIMO beam combinations for multiple MIMO spatial streams basedon SNIR and sends back to the initiator. Alternatively, the respondersends the channel measurements to the initiator that selects the MIMOcombination. Finally, beam refinement is performed to fine-tune theantenna beams for improved signal quality. In one novel aspect, theleakage from one spatial stream into the receive beam of another spatialstream is considered as interference for SNIR calculation.

In a second embodiment, an initiator and a responder exchangebeam-training parameters to start a MIMO training procedure. During TXsector sweeping, the initiator sends training packets through all TXsectors, while the responder receives the training packets withomni-direction beam. The responder sends back a set of selected TXsectors with good received signal quality and the corresponding channelmeasurements. During RX sector sweeping, the initiator sends trainingpacket using each selected TX sector, while the responder receives thetraining packets through all RX sectors. The responder selects one RXsector with good received signal quality for each selected TX sector.The responder determines the best MIMO beam combinations for multipleMIMO spatial streams based on SNIR and sends back to the initiator.Alternatively, the responder sends the channel measurements to theinitiator that selects the MIMO beam combinations. Finally, beamrefinement is performed to fine-tune the antenna beams for improvedsignal quality. In one novel aspect, the leakage from one spatial streaminto the receive beam of another spatial stream is considered asinterference for SNIR calculation.

In multiple antenna beamforming operation, simultaneous transmission andreception of multiple streams (spatial multiplexing) are supported. Inone example, each spatial stream is transmitted from a TX sector of a TXantenna to an RX sector of a RX antenna and different spatial streamsare transmitted from different TX antenna and received by different RXantenna. Thus, each MIMO combination consists of select N TX sectors andN RX sectors for transmitting N spatial streams. The selected N TXsectors are from N different TX antennas, and the selected RX sectorsare from N RX antenna. In another example, each spatial stream istransmitted from a TX beamformer to an RX beamformer and differentspatial streams are transmitted from different TX beamformer andreceived by different RX beamformer. Thus, each MIMO combinationconsists of select N TX sectors and N RX sectors for transmitting Nspatial streams. The selected N TX sectors are from N different TXbeamformers, and the selected RX sectors are from N RX beamformers. Theselection criteria includes not only signal quality, but also considersmutual interference and leakage among multiple MIMO spatial streams toimprove overall MIMO performance. Simultaneous RX and/or TX training arealso supported to reduce training time.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a MU-MIMO operation with antenna beam training formultiple spatial streams in a wireless system in accordance with onenovel aspect.

FIG. 2 illustrates a simplified block diagram of a wireless device in awireless system in accordance with one novel aspect.

FIG. 3 illustrates a message/signal exchange flow of a first embodimentof antenna beam training for MIMO operation.

FIG. 4A illustrates a first step of the first embodiment of antenna beamtraining.

FIG. 4B illustrates a second step of the first embodiment of antennabeam training.

FIG. 4C illustrates a third step of the first embodiment of antenna beamtraining.

FIG. 5 illustrates a message/signal exchange flow of a second embodimentof antenna beam training for MIMO operation.

FIG. 6A illustrates a first step of the second embodiment of antennabeam training.

FIG. 6B illustrates a second step and a third step of the secondembodiment of antenna beam training.

FIG. 7 is a flow chart of a first embodiment of a method of antenna beamtraining for MIMO operation in accordance with a novel aspect.

FIG. 8 is a flow chart of a second embodiment of a method of antennabeam training for MIMO operation in accordance with a novel aspect.

FIG. 9 illustrates MIMO transmission for IEEE 802.11ay.

FIG. 10 illustrates a first part of beamforming training procedure formultiple antennas.

FIG. 11 illustrates a second part of beamforming training procedure formultiple antennas.

FIG. 12 illustrates one embodiment of SLS phase in BTI and A-BFT and BRPsetup sub-phase.

FIG. 13 illustrates one embodiment of SLS phase in DTI and BRP setupsub-phase.

FIG. 14 illustrates a first embodiment of MIDC sub-phase with MID and BCsub-phases.

FIG. 15 illustrates a second embodiment of MIDC sub-phase with MID andBC sub-phases.

FIG. 16A illustrates a first embodiment of MID sub-phase only.

FIG. 16B illustrates a second embodiment of MID sub-phase only.

FIG. 17A illustrates a first embodiment of BC sub-phase only.

FIG. 17B illustrates a second embodiment of BC sub-phase only.

FIG. 18 is a flow chart of a first embodiment of a method of beamformingtraining for multiple antenna operation in accordance with a novelaspect.

FIG. 19 is a flow chart of a second embodiment of a method ofbeamforming training for multiple antenna operation in accordance with anovel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates a MU-MIMO operation with antenna beam training formultiple spatial streams in a wireless system 100 in accordance with onenovel aspect. Wireless system 100 comprises an initiator 101 and aresponder 102. Both initiator 101 and responder 102 are equipped withantenna arrays to support MIMO operation for multiple spatial streams.To enable MIMO operation, initiator 101 signals to responder 102 tostart a MIMO training with a list of MIMO training parameters. Thepurpose of MIMO training is for antenna array beamforming, where bothtransmitting antennas and receiving antennas are steered with the bestbeam combinations to increase data rate and enhance signal quality.

In the example of FIG. 1, the intended direction is initiator 101 is thetransmitter of MIMO signal and responder 102 is the receiver of MIMOsignal. Note that an initiator can also initiate a MIMO training inwhich the initiator is the receiver of MIMO signal. In step 111,initiator 101 performs TX sector sweeping, where training packets aretransmitted to responder 102 through the TX sectors, each sectorcorresponds to a specific TX antenna beam/pattern (e.g.,direction/weight). During RX sector sweeping, training packets aretransmitted from initiator 101 to responder 102, which sweeps throughthe RX sectors, each sector corresponds to a specific RX antennabeam/pattern (e.g., direction/weight). In step 112, responder 102records the received signal quality (e.g., signal-to-noise ratio (SNR))and determines a number of beam combinations (selected TX and RX sectorpairs) based on the results of TX sector sweep and RX sector sweep. Thenumber of beam combinations needs to be greater or equal to the numberof spatial streams. In step 113, from the selected TX and RX sectorpairs, responder 102 determines the best MIMO beam combinations for themultiple MIMO spatial streams based on signal-to-(noise+interference)ratio (SNIR) criteria.

In one novel aspect, the simple and efficient beam training methodoperates in high SNR condition for reliable operation. Furthermore, byconsidering mutual interference or leakage among the multiple MIMOspatial streams, the MIMO beam combination selection is more accurate toimprove overall MIMO performance.

FIG. 2 illustrates a simplified block diagram of a wireless device 201in a wireless system in accordance with one novel aspect. Wirelessdevice 201 comprises memory 202, a processor 203, a scheduler 204, aMIMO encoder 205, a beamformer/precoder 206, a channel estimation module207, and a plurality of transceivers 211-214 coupled to a plurality ofantennas 215-218, respectively. The wireless device receives RF signalsfrom the antenna, converts them to baseband signals and sends them tothe processor. RF transceiver also converts received baseband signalsfrom the processor, converts them to RF signals, and sends out to theantenna. Processor 203 processes the received baseband signals andinvokes different functional modules to perform features in the device.Memory 202 stores program instructions and data to control theoperations of the device. In one embodiment, the transceivers are a typeof transmit and receive frontend electronics. FIG. 2 further illustratesfunctional modules in the wireless device that carry out embodiments ofthe current invention, which includes a scheduler 204, a MIMOencoder/decoder 205, a MIMO precoder/beamformer 206, and a channelestimation module 207.

FIG. 3 illustrates a message/signal exchange flow of a first embodimentof antenna beam training for MIMO operation in a wireless communicationssystem 300. Wireless communications system 300 comprises an initiator301 and a responder 302. In step 310, the initiator sends a MIMObeam-training message to the responder to start a MIMO trainingprocedure. The beam-training message comprises MIMO training parameterssuch as the number of TX sectors, the number of RX sectors, the numberof MIMO spatial streams, the number of candidate beam combinations, andother relevant parameters. For example, the duration and timing oftraining packets may be included as part of the parameters. In theexample of FIG. 3, the initiator is the transmitter of MIMO signal.However, an initiator can also initiate a MIMO training in which it isthe receiver of MIMO signal.

In step 311, during TX sector sweeping, initiator 301 starts sendingtraining packets to responder 302. Each training packet is a shortpacket designed for beam training—allowing the receiver to measure thereceived signal quality, but not carrying extra data payload to reducetime. For TX sector sweeping, the training packets are sent through allthe TX sectors—one packet per sector with a gap (inter-frame spacing)between consecutive training packets. Responder 302 receives thetraining packets with an omni-direction antenna pattern and records thereceived signal quality for each TX sector. In step 312, responder 302feedbacks a set of selected TX sectors with good received signal qualityto initiator 301. In step 313, RX sector sweeping is performed.Initiator 301 transmits training packets with a semi-omni antennapattern while responder 302 sweep through all the RX sectors with dwelltime of each RX sector corresponding to the training packet duration andtiming. Responder 302 again records the received signal quality for eachRX sector. In step 314, responder 302 optionally feedbacks the candidatebeam combinations (e.g., a list of TX-RX sector pairs) to initiator 301.Based on the results of TX sector sweep and RX sector sweep, theselection of RX sectors is based on signal quality (e.g., SNR).

In step 315, the initiator and the responder start sweeping the selectedTX sectors and the selected RX sectors together for beam combinationtraining. During the beam combination training, the initiator transmitsa training packet through one of the selected TX sectors while theresponder receives the training packet through the paired RX sector inone beam combination. Because the initiator already knows the selectedTX-RX sector pairs, it knows how many times to send the training packetsfor each selected TX sector. In an alternative embodiment, the respondermight not feedback the beam combinations in step 314. As long as theinitiator knows the number of candidate beam combinations, it stillknows how many times to send the training packets for each selected TXsector for beam combination training. The responder records the signalquality for each selected TX-RX sector pair during the beam combinationtraining.

In step 316, responder 302 determines the best MIMO beam combinationsfor the multiple MIMO spatial streams. If there are two MIMO spatialstreams, then two best MIMO beam combinations are determined. Forspatial multiplexing, the best MIMO beam combinations are determinedbased on the highest SNIR. For spatial combining, the best MIMO beamcombinations are determined based on the highest total combined power(SUM power). In step 317, responder 302 feedbacks the best MIMO beamcombinations to initiator 301. Finally, in step 318, initiator 301 andresponder 302 perform beam refinement, which fine-tunes the antennabeams for improved pointing accuracy and higher signal quality. Moredetails of the first MIMO training embodiment are now described belowaccompanied with FIGS. 4A-4C.

FIG. 4A illustrates a first step of the first embodiment of antenna beamtraining. The first step involves TX sector sweeping after initializinga MIMO training between an initiator and a responder. In the example ofFIG. 4A, the initiator transmits training packets through totalthirty-two (32) TX sectors—sectors 1 to 32. The responder receives thetraining packets with an omni-direction beam. The responder then selectsfour TX sectors with the best signal quality (e.g., TX sectors 1, 9, 25,and 28). The responder also sends the selected TX sectors back to theinitiator.

FIG. 4B illustrates a second step of the first embodiment of antennabeam training. The second step involves RX sector sweeping. In theexample of FIG. 4B, the initiator transmits training packets using anomni-direction beam to the responder, while the responder receives thetraining packets sweeping through total sixteen (16) RX sectors—sectors1 to 16. The responder then selects four RX sectors with the best signalquality (e.g., RX sectors 3, 6, 8, and 15).

FIG. 4C illustrates a third step of the first embodiment of antenna beamtraining. The third step involves beam combination training using theselected TX sectors and the selected RX sectors. In the example of FIG.4C, the initiator transmits training packets sweeping through theselected TX sectors (1, 9, 25, and 28), while the responder receives thepackets sweeping through the selected RX sectors (3, 6, 8, and 15). Theresponder then records the signal quality (SNR) for all sixteen (4 TXsectors×4 RX sectors=16) beam combinations, as depicted by table 430.

The best MIMO beam combinations for multiple MIMO spatial streams areselected from the sixteen beam combinations. The best beam combinationtypically means the highest signal quality (SNR). However, in order toselect the best beam combinations for multiple spatial streams, theselection criteria needs to include the interference or leakage betweenthe spatial streams. Suppose TX1-RX3 sector pair and TX28-RX6 sectorpair are selected as the MIMO beam combinations for two MIMO spatialstreams SS1 and SS2, respectively. The received signal power from TX1 toRX6 becomes the interference to the TX28-RX6 pair, and the receivedsignal power from TX28 to RX3 becomes the interference to the TX1-RX3pair. After considering the mutual interference or leakage, theresponder determines the best two beam combinations for two spatialstreams.

FIG. 5 illustrates a message/signal exchange flow of a second embodimentof antenna beam training for MIMO operation in a wireless communicationssystem 500. Wireless communications system 500 comprises an initiator501 and a responder 502. In step 510, the initiator sends a MIMObeam-training message to the responder to start a MIMO trainingprocedure. The beam-training message comprises MIMO training parameterssuch as the number of TX sectors, the number of RX sectors, the numberof MIMO spatial streams, the number of candidate beam combinations, andother relevant parameters. For example, the duration and timing oftraining packets may be included as part of the parameters. In theexample of FIG. 5, the initiator is the transmitter of MIMO signal.However, an initiator can also initiate a MIMO training in which it isthe receiver of MIMO signal.

In step 511, during TX sector sweeping, initiator 501 starts sendingtraining packets to responder 502. Each training packet is a shortpacket designed for beam training—allowing the receiver to measure thereceived signal quality, but not carrying extra data payload to reducetime. For TX sector sweeping, the training packets are sent through allthe TX sectors—one packet per sector with a gap (inter-frame spacing)between consecutive training packets. Responder 502 receives thetraining packets with omni-direction antenna pattern and records thereceived signal quality for each TX sector. In step 512, responder 502feedbacks a set of selected TX sectors with good received signal qualityto initiator 501. In step 513, RX sector sweeping is performed. In thesecond embodiment, instead of using omni-direction beam for transmittingtraining packets, initiator 501 transmits through one of the selected TXsectors a number of training packets (corresponding to the number of RXsectors to be swept), while responder 502 sweeps through all the RXsectors. The initiator repeats this process for each selected TX sectorwhile the responder sweeps through all the RX sectors for each selectedTX sector. The dwell time of each RX sector corresponds to a trainingpacket duration and timing. Responder 502 again records the receivedsignal quality and selects one RX sector with good signal quality foreach selected TX sector.

In step 514, responder 502 determines the best MIMO beam combinationsfor multiple MIMO spatial streams based on the results of the TX sectorsweeping and the RX sector sweeping. No additional beam combinationtraining is necessary in the second embodiment. If there are two MIMOspatial streams, then the two best MIMO beam combinations aredetermined. For spatial multiplexing, the best MIMO beam combinationsare determined based on the highest SNIR. For spatial combining, thebest MIMO beam combinations are determined based on the highest totalcombined power (SUM power). In step 515, responder 502 feedbacks thebest MIMO beam combinations to initiator 501. Finally, in step 516,initiator 501 and responder 502 perform beam combination refining, whichfine-tunes the antenna beams for improved pointing accuracy and highersignal quality. More details of the second MIMO training embodiment arenow described below accompanied with FIGS. 6A-6B.

FIG. 6A illustrates a first step of the second embodiment of antennabeam training. The first step involves TX sector sweeping afterinitializing a MIMO training between an initiator and a responder. Inthe example of FIG. 6A, which is similar to FIG. 4A of the firstembodiment, the initiator transmits training packets through totalthirty-two (32) TX sectors—sectors 1 to 32. The responder receives thetraining packets with an omni-direction beam. The responder then selectsfour TX sectors with the best signal quality (e.g., TX sectors 1, 9, 25,and 28). The responder also sends the selected TX sectors back to theinitiator.

FIG. 6B illustrates a second step and a third step of the secondembodiment of antenna beam training. The second step involves RX sectorsweeping. In the example of FIG. 6B, the initiator transmits trainingpackets using each of the selected TX sector (1, 9, 25, and 28) to theresponder, while the responder receives the training packets sweepingthrough total sixteen (16) RX sectors—sectors 1 to 16. The responderthen selects one RX sector with the highest signal quality for each ofthe selected TX sector (e.g., RX sectors 3, 6, 8, and 15 for TX sectors1, 9, 25, and 28 respectively).

The third step involves the final selection of the best MIMO beamcombinations. The already selected four TX-RX sector pairs are based onsignal quality. In order to find the best beam combinations for multiplespatial streams, the selection criteria needs to include the mutualinterference or leakage between the spatial streams. After consideringthe mutual interference or leakage, the best two beam combinations arefinally determined. For example, TX1-RX3 sector pair is selected for afirst spatial stream SS#1, and TX28-RX6 sector pair is selected for asecond spatial stream SS#2. In this case, the received signal power fromTX1 to RX6 becomes the interference to the TX28-RX6 pair, and thereceived signal power from TX28 to RX3 becomes the interference to theTX1-RX3 pair. Based on both the SNR and SNIR information, the TX1-RX3and TX28-RX6 beam combinations are the best beam combinations for MIMOSS#1 and SS#2.

Note that the second embodiment overall requires more training packetsas compared to the first embodiment. From implementation perspective,the difference between the first embodiment and the second embodiment iswhether the transmitting device needs to send training packets usingomni-direction antenna pattern. The second embodiment does not requirethe implementation of semi-omni transmit antenna. In general, receiveromni-pattern is easier to form since one single antenna element wouldprovide near omni pattern. The receiver omni-antenna gain is lower thanthe array antenna gain by the array gain. For transmitter, however, itis difficult to provide an omni-pattern. If a single antenna is used forgenerating omni-directional pattern, not only the antenna gain isreduced by the array gain but also the power gain is reducedproportional to how many power amplifiers are not used. As a result, theeffective isotropic radiated power (EIRP) is reduced by array gain pluspower gain.

FIG. 7 is a flow chart of a first embodiment of a method of antenna beamtraining for MIMO operation in accordance with a novel aspect. In step701, an initiator communicates with a responder a MIMO beam-trainingmessage to start a MIMO training procedure in a wireless network. Theinitiator is the transmitter of MIMO signal and the responder is thereceiver of MIMO signal. Alternatively, the receiver of MIMO signal mayalso initiate the MIMO training procedure. In step 702, TX sectorsweeping is started. The initiator sends training packets through all TXsectors, and the responder receives the training packets withomni-direction beam. In step 703, the responder sends a set of selectedTX sectors with good received signal quality back to the initiator. Instep 704, RX sector sweeping is started. The initiator sends trainingpackets with omni-direction beam, and the responder receives thetraining packets through all RX sectors. The responder then determines aset of selected RX sectors with good received signal quality. In step705, beam combination training is started. The initiator and theresponder sweep through the selected TX sectors and RX sectors together.The responder records the received signal quality. In step 706, theresponder determines the best MIMO beam combinations for multiple MIMOspatial streams based on signal quality and based on interference orleakage among the different spatial streams. In step 707, beamrefinement is performed to fine-tune the antenna beams for improvedsignal quality.

FIG. 8 is a flow chart of a second embodiment of a method of antennabeam training for MIMO operation in accordance with a novel aspect. Instep 801, an initiator communicates with a responder a MIMObeam-training message to start a MIMO training procedure in a wirelessnetwork. The initiator is the transmitter of MIMO signal and theresponder is the receiver of MIMO signal. Alternatively, the receiver ofMIMO signal may also initiate the MIMO training procedure. In step 802,TX sector sweeping is started. The initiator sends training packetsthrough all TX sectors, and the responder receives the training packetswith omni-direction beam. In step 803, the responder sends a set ofselected TX sectors with good received signal quality back to theinitiator. In step 804, RX sector sweeping is started. The initiatorsends training packets using one of the selected TX sectors, and theresponder receives the training packets through all RX sectors. Theinitiator repeats the process for each selected TX sector. The responderthen determines a set of selected RX sectors with good received signalquality for each selected TX sector. In step 805, the responderdetermines the best MIMO beam combinations for multiple MIMO spatialstreams based on signal quality and based on interference or leakageamong the different spatial streams. In step 806, beam refinement isperformed to fine-tune the antenna beams for improved signal quality.

Multiple Antenna Beamforming Operation

In IEEE 802.11ad, the beamforming training protocol supports multipleantenna selection operation. In IEEE 802.11ay, MIMO operation isproposed to be a key feature that requires multiple antennas (orbeamformers). In addition, multiple antenna beamforming operation needsto support multiple antenna TX and/or RX beamforming, when multipleantenna device communicates with single antenna device. FIG. 9illustrates MIMO transmission for IEEE 802.11ay. In the example of FIG.9, initiator 901 comprises multiple antenna arrays 911 and 912, andresponder 902 comprises multiple antenna arrays 921 and 922. MIMOoperation involves simultaneous transmission and reception of multiplespatial streams (spatial multiplexing). For N×N MIMO system, the key isto establish N independent spatial links between TX and RX antennasbased on IEEE 802.11ad beamforming framework. Each array antenna istypically configured to form a single sector/beam at a time to be usedfor transmission or reception of a single spatial stream. IEEE 802.11adbeamforming training procedure therefore needs to be modified in such away that no any selected TX/RX sectors come from the same TX/RX antennaor the same TX/RX beamformer. Inter-antenna leakage should also beconsidered in the beamforming training procedure for MIMO operation.

In one example, each spatial stream is transmitted from a TX sector of aTX antenna to an RX sector of a RX antenna and different spatial streamsare transmitted from different TX antennas and received by different RXantennas. Thus, MIMO beam combination training consists of selecting NTX sector and RX sector pairs for transmitting N spatial streams. Theselected N TX sectors are from N different TX antennas, and the selectedRX sectors are from N RX antennas. In another example, each spatialstream is transmitted from a TX beamformer to an RX beamformer anddifferent spatial streams are transmitted from different TX beamformersand received by different RX beamformers. Thus, MIMO beam combinationtraining consists of selecting N TX sectors and N RX sectors fortransmitting N spatial streams. The selected N TX sectors are from Ndifferent TX beamformers, and the selected RX sectors are from N RXbeamformers. It is also possible to form a sector/beam from more thanone antenna arrays for supporting of a spatial stream. For array antennarealization, it is also possible to attach multiple beamformers to thesame set of physical antenna elements for forming multiple arrays(shared array) that can support multiple spatial streams. For the sakeof convenient in discussion, we use the term “antenna” or “beamformer”to represent an apparatus that supports a spatial stream.

MIMO transmitter and receiver are capable of simultaneously transmittingor receiving through multiple antennas. Reduced the number of trainingframes (SSW) or fields (TRN-R and TRN-T) thus can be achieved. First,simultaneous training of multiple RX antennas can be performed bytransmitting one training frame or field, and receiving simultaneouslyby multiple RX antennas. Second, simultaneous training of multiple TXantennas can be performed by transmitting resolvable transmit trainingframes or fields from multiple TX antennas simultaneously, and receiverresolving training signal from each TX antenna (e.g., each antennatransmit training frames or fields modulated by orthogonal vector, suchas the row vectors in a p matrix). Third, Simultaneous training ofmultiple receiving STAs (MU-MIMO) can be performed by transmitting onetraining frame or field, and receiving simultaneously by multiple RXreceiving STAs.

Specifically, in IEEE 802.11ad, a training field is transmitted for eachTX sector and RX sector pair. For training receive sector with each TXsector, a total of S_(TOTAL) training fields are needed, where S_(TOTAL)is the total number of RX sectors across all RX antennas. For MIMOoperation, however, since the N RX antennas can receive simultaneously,it is possible to transmit to multiple RX sectors simultaneously tospeed up RX sector training by receiving with RX sectors belongs todifferent RX antennas or different RX beamformers. As a result, only atotal of S_(MAX) training fields are needed for each TX sector, whereS_(MAX) is the maximum number of RX sectors per RX antenna among N RXantennas. Note that unlike simultaneous TX sector training where thetraining frame or field need to be modified with orthogonal vectors,simultaneously RX sector training can employ the prior art trainingframe or training field provided that both transmitter and receiver knowa priori about the configuration of the intended training operation.

FIG. 10 illustrates a first part of beamforming training procedure formultiple antennas between an initiator and a responder. The initialoperation can follow the IEEE 802.11ad beamforming protocol, calledsector level sweep (SLS), to establish an initial link and then exchangeIEEE 802.11ay beamforming capability. During the initiator I-TXSS, theinitiator first transmits DMG beacon frames during beacon transmissioninterval (BTI). During the responder R-TXSS, the responder transmitssector sweep (SSW) frames and receives SSW feedback from the initiatorduring A-BFT. The best transmit sector is feedback to initiator viaresponder's SSW frames (e.g., SSW frame 1010). The best transmit sectoris feedback to responder via initiator's SSW feedback frames (e.g., SSWfeedback frame 1020). After the initial link is established, theinitiator and the responder then performs beamforming capabilityexchange as depicted by step 1030, during which MIMO beamformingcapabilities and parameters for multiple antenna operation areexchanged. In one example, the MIMO beamforming capabilities andparameters includes a number of TX/RX antennas, a number of TX sectorsfor each TX antenna, a number of RX sectors for each RX antenna, anumber of MIMO spatial streams supported, a pre-determined number ofMIMO beam combinations to be trained, and MIMO training capabilityinformation, e.g., whether the initiator and the responder is capable ofsimultaneous TX and RX training. MIMO training can start after SLS inMID/BC setup frame exchange, by explicitly request in the training framemessage exchange or using an indicator in the frame.

FIG. 11 illustrates a second part of beamforming training procedure formultiple antennas between the initiator and a responder. Afterbeamforming capability exchange, there may be a sector level sweep (SLS)phase (1110), which can be performed in DTI to renew the antennatraining for changing channel condition. Complete sector sweep orupdating of stale sector training is performed during this SLS phase.Next is the beam refinement protocol (BRP) setup phase (1120), duringwhich the initiator and the responder perform beam refinementtransaction consisting of a series of beam refinement requests andresponses. Note that during the setup phase, the initiator can requestthe responder to feedback channel measurements and/or selected transmitantenna sectors obtained during SLS and use this information todetermine the selected TX sector for MIMO training. Next is the optionalmultiple antenna ID (MID) sub-phase (1130), during which RX sectortraining with quasi-omni TX antennas is performed. Finally, a beamcombination (BC) sub-phase (1130) is performed, which includesbeamforming training on the possible pairings of the selected TXsector/antennas and the selected RX sector/antennas, followed by CSIfeedback or sector/antenna selection.

The beamforming training protocol here described should be flexible tobe applicable to a single channel operation as well as more flexiblechannel bonding (wideband, 2×, 3×, 4× bandwidth) operation. In otherwords, the proposed operation should support different combination ofSSW, beacon, BRP frames employing single channel signal format,duplicate signal format, or wideband signal format. A preferredembodiment would be using the single channel operation for SLS (sectorlevel training) such as during I_TXSS or R-TXSS while employing awideband (channel bonded) frame (waveform) for BRP frames to allow formore accurate channel measurement or beam combination training overwideband channel. Another embodiment is to use duplicate waveform forSSW or beacon for SLS and employs channel bonded (wideband) for BRFframe.

FIG. 12 illustrates one embodiment of SLS phase in BTI and A-BFT and BRPsetup sub-phase. During SLS (BTI+A-BFT), the initiator transmits throughall TX sectors and indicates simultaneous RX sector training in I-TXSS.The responder receives simultaneously through all RX antennas beingconfigured to a quasi-omni pattern. The responder then transmits throughall TX sectors in R-TXSS, and the initiator receives simultaneouslythrough all RX antennas being configured to a quasi-omni pattern. Afterthe BRP setup sub-phase (depicted by point {circle around (1)} in FIG.12), the initiator then chooses a small set of TX sectors per TX antennabased on the channel measurements or sector ID feedback from theresponder (e.g., SNR feedback or sector ID contained in BRP 1210) aswell as other additional information.

FIG. 13 illustrates one embodiment of SLS phase in DTI and BRP setupsub-phase. During SLS (DTI), the initiator transmits through all TXsectors and indicates simultaneous RX sector training in I-TXSSexplicitly or implicitly as agreed upon during the initial beamformingcapability exchange. The responder receives simultaneously through allRX antennas being configured to a quasi-omni pattern. The responder thentransmits through all TX sectors in R-TXSS, and the initiator receivessimultaneously through all RX antennas being configured to a quasi-omnipattern. After the BRP setup sub-phase (depicted by point {circle around(1)} in FIG. 13), the initiator then chooses a small set of TX sectorsper TX antenna based on the channel measurements or sector ID feedbackfrom the responder (e.g., SNR feedback or sector ID contained in BRP1310) as well as other additional information.

FIG. 14 illustrates a first embodiment of MIDC sub-phase with MID and BCsub-phases. During the I-MID sub-phase, the initiator first transmitsBRP frames through all TX antennas being configured to a wide pattern.The responder then receives simultaneously through all RX antennas, eachsweeping all RX sectors. At point {circle around (1)}, the responderchooses a small set of RX sectors per RX antenna based on link quality.The responder also feedbacks the number of the chosen RX sectors to theinitiator (e.g., via BRP 1410). During the I-BC sub-phase, the initiatortransmits BRP frames through all possible pairings from the chosen TXsectors in I-TXSS, and the responder receives simultaneously through allRX antennas, each sweeping the chosen RX sectors in I-MID. At point{circle around (2)}, the responder determines the best N TX/RX sectorcombinations (pairings) in such a way so that no any selected TX/RXsectors come from the same TX/RX antenna, and feedbacks the chosen N TXsector and RX sector pairs to the initiator (e.g., via BRP 1420). Forexample, the responder may use the channel measurements to computesignal-to-leakage ratio and spatial capacity (i.e., sum of each spatialstream) for determine the best TX/RX sector combinations.

FIG. 15 illustrates a second embodiment of MIDC sub-phase with MID andBC sub-phases. During the I-MID sub-phase, the initiator first transmitsBRP frames through all TX antennas being configured to a wide pattern.The responder then receives simultaneously through all RX antennas, eachsweeping all RX sectors. At point {circle around (1)}, the responderchooses a small set of RX sector per RX antenna based on link quality(e.g., SNR) and then feedbacks the number of chosen RX sectors to theinitiator (via BRP 1510). During the I-BC sub-phase, the initiatortransmits BRP frames through possible pairings of the chosen TX sectorsin I-TXSS, and the responder receives simultaneously through all RXantennas, each sweeping the chosen RX sectors in I-MID. The responderthen feedbacks the channel measurements to the initiator (via BRP 1520).At point {circle around (2)}, the initiator determines the best N TX/RXsector combinations based on channel measurements in such a way so thatno any selected TX/RX sectors come from the same TX/RX antenna, andfeedbacks the chosen N TX sector and RX sector pairs to the responder.For example, the initiator may use the channel measurements to computesignal-to-leakage ratio and spatial capacity (i.e., sum of each spatialstream) for determine the best TX/RX sector combinations.

FIG. 16A illustrates a first embodiment of MIDC sub-phase with MIDsub-phase only. During the I-MID sub-phase, the initiator firsttransmits BRP frames through all TX sectors being configured to a widepattern. The responder then receives simultaneously through all RXantennas, each sweeping all RX sectors. At point {circle around (1)},the responder determines a small set of RX sectors per RX antenna basedon link quality and feedbacks the chosen RX sector to the initiator (viaBRP 1610).

FIG. 16B illustrates a second embodiment of MIDC sub-phase with MIDsub-phase only. During the I-MID sub-phase, the initiator firsttransmits BRP frames through all TX sectors being configured to a widepattern. The responder then receives simultaneously through all RXantennas, each sweeping all RX sectors. At point {circle around (1)},the responder feedbacks the channel measurements to the initiator (viaBRP 1620). At point {circle around (2)}, the initiator determines asmall set of RX sectors based on channel measurements, and feedbacks thechosen RX sectors to the responder.

FIG. 17A illustrates a first embodiment of BC sub-phase only. During theI-BC sub-phase, the initiator first transmits BRP frames through allchosen TX sectors in I-TXSS. The responder then receives simultaneouslythrough all RX antennas, each sweeping all RX sectors. At point {circlearound (1)}, the responder determines the best N TX/RX sectorcombinations in such a way so that no any selected TX/RX sectors comefrom the same TX/RX antenna or beamformer, and feedbacks the chosen N TXsector and RX sector pairs to the initiator (via BRP 1710).

FIG. 17B illustrates a second embodiment of BC sub-phase only. Duringthe I-BC sub-phase, the initiator first transmits BRP frames through allchosen TX sectors in I-TXSS. The responder then receives simultaneouslythrough all RX antennas, each sweeping all RX sectors. At point {circlearound (1)}, the responder feedbacks the channel measurements to theinitiator (via BRP 1720). At point {circle around (2)}, the initiatordetermines the best N TX/RX sector combinations based on channelmeasurements in such a way so that no any selected TX/RX sectors comefrom the same TX/RX antenna or beamformer, and feedbacks the chosen N TXsector and RX sector pairs to the responder. For example, the initiatormay use the channel measurements to compute signal-to-leakage ratio andspatial capacity (i.e., sum of each spatial stream) for determine thebest TX/RX sector combinations.

Suppose that N TX/RX sector combinations are selected as:

{(k ₀ ,l _(m) ₀ ),(k ₁ ,l _(m) ₁ ), . . . ,(k _(N-1) ,l _(m) _(N-1) )}

where

-   -   (k_(i)l_(m) _(i) ) stands for a combination of TX sector k_(i)        of TX antenna i and RX sector l_(m) _(i) of RX antenna m_(i),        and m_(s)≠m_(t) if s≠t.    -   The best N TX/RX sector combinations are determined which give        the highest link capacity (throughput).

FIG. 18 is a flow chart of a first embodiment of a method of beamformingtraining for multiple antenna operation in accordance with a novelaspect. In step 1801, an initiator communicates with a responder a MIMObeam-training message to start a MIMO training procedure in a wirelessnetwork. The initiator is the transmitter of MIMO signal and theresponder is the receiver of MIMO signal. Alternatively, the receiver ofMIMO signal may also initiate the MIMO training procedure. In step 1802,TX sector sweeping is started. The initiator sends training packetsthrough all TX sectors of all TX antennas, and the responder receivesthe training packets simultaneously through all RX antennas withomni-direction beam. In step 1803, the responder sends a set of selectedTX sectors for each TX antenna with good received signal quality back tothe initiator. Alternatively, the responder may feedback the signal tonoise radio (SNR) info to the initiator for TX sector selection.

In step 1804, RX sector sweeping is started. The initiator sendstraining packets with omni-direction beam, and the responder receivesthe training packets simultaneously through all RX antennas, eachsweeping all RX sectors. The responder then determines a set of selectedRX sectors with good received signal quality and feedback to theinitiator. In step 1805, beam combination training is started. Theinitiator and the responder sweep through the selected TX sectors and RXsectors together. The responder records the received signal quality. Instep 1806, the responder determines the best MIMO beam combinations formultiple MIMO spatial streams based on signal quality and based oninterference or leakage among the different spatial streams.Alternatively, the responder may feedback the SNIR info to the initiatorfor the best beam combination determination. The best beam combinationsare determined in such a way that no any selected TX/RX sectors comefrom the same TX/RX antenna or beamformers.

FIG. 19 is a flow chart of a second embodiment of a method ofbeamforming training for multiple antenna operation in accordance with anovel aspect. In step 1901, an initiator communicates with a responder aMIMO beam-training message to start a MIMO training procedure in awireless network. The initiator is the transmitter of MIMO signal andthe responder is the receiver of MIMO signal. Alternatively, thereceiver of MIMO signal may also initiate the MIMO training procedure.In step 1902, TX sector sweeping is started. The initiator sendstraining packets through all TX sectors of all antennas, and theresponder receives the training packets simultaneously through all RXantennas with omni-direction beam. In step 1903, the responder sends aset of selected TX sectors for each TX antenna with good received signalquality back to the initiator. Alternatively, the responder may feedbackthe signal to noise ratio (SNR) info to the initiator for TX sectorselection.

In step 1904, RX sector sweeping is started. The initiator sendstraining packets using one of the selected TX sectors, and the responderreceives the training packets simultaneously through all RX antennas,each sweeping all RX sectors. The initiator repeats the process for eachselected TX sector. The responder then determines a set of selected RXsectors with good received signal quality for each selected TX sector.In step 1905, the responder determines the best MIMO beam combinationsfor multiple MIMO spatial streams based on signal quality and based oninterference or leakage among the different spatial streams.Alternatively, the responder may feedback the signal to noise ratio(SNIR) info to the initiator for beam combination determination. Thebest beam combinations are determined in such a way that no any selectedTX/RX sectors come from the same TX/RX antenna or beamformers. In step1906, beam refinement is performed to fine-tune the antenna beams forimproved signal quality.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method comprising: (a) initiating a multipleinput and multiple output (MIMO) training procedure in a wirelessnetwork; (b) transmitting training frames using all TX sectors during TXsector sweeping for obtaining a set of selected TX sectors for each TXantenna, wherein each of the TX sectors corresponds to a specific TXantenna beam; (c) obtaining a set of selected RX sectors for each RXantenna, wherein each of the RX sectors corresponds to a specific RXantenna beam; (d) performing MIMO beam combination training based onpairings of the selected TX and RX sectors, wherein each of the MIMObeam combinations includes one TX sector from the set of selected TXsectors and one RX sector from the set of selected RX sectors; and (e)obtaining multiple best MIMO beam combinations for multiple MIMO spatialstreams based on the MIMO beam combination training.
 2. The method ofclaim 1, wherein the initiating in (a) involves communicating a messagethat comprises at least one of a number of TX/RX antennas, a number ofTX/RX sectors for each TX/RX antenna, a number of MIMO spatial streamssupported, a number of MIMO beam combinations to be trained, and MIMOtraining capability information.
 3. The method of claim 1, wherein theselected TX and RX sectors are determined based on signal to noiseratios (SNRs), and wherein the multiple best MIMO beam combinations aredetermined based on signal to noise plus interference ratios (SNIRs),channel measurement, or channel measurement feedbacks.
 4. The method ofclaim 1, wherein one TX/RX sector is beamformed from multiple TX/RXantennas or beamformers.
 5. The method of claim 1, wherein the trainingframes are transmitted simultaneously by multiple TX antennas.
 6. Themethod of claim 1, wherein training frames are transmitted via an omnitransmit beam for obtaining the set of selected RX sectors for each RXantenna.
 7. The method of claim 1, wherein the set of selected TXsectors is smaller or equal to all TX sectors, and wherein the set ofselected RX sectors is smaller or equal to all RX sectors.
 8. The methodof claim 1, wherein no more than one TX sector of the best MIMO beamcombinations is selected from the same TX antenna or TX beamformer, andwherein no more than one RX sector of the best MIMO beam combinations isselected from the same RX antenna or RX beamformer.
 9. A methodcomprising: (a) initiating a multiple input and multiple output (MIMO)training procedure in a wireless network; (b) receiving training framesusing omni-direction antenna pattern during TX sector sweeping fordetermining a set of selected TX sectors for each TX antenna, whereineach of the TX sectors corresponds to a specific TX antenna beam; (c)determining a set of selected RX sectors for each RX antenna, whereineach of the RX sectors corresponds to a specific RX antenna beam; (d)performing MIMO beam combination training based on the selected TX andRX sectors, wherein each of the MIMO beam combinations includes one TXsector from the set of selected TX sectors and one RX sector from theset of selected RX sectors; and (e) obtaining multiple best MIMO beamcombinations for multiple MIMO spatial streams based on the results ofthe MIMO beam combination training.
 10. The method of claim 9, whereinthe initiating in (a) involves communicating a message that comprises atleast one of a number of TX/RX antennas, a number of TX/RX sectors foreach TX/RX antenna, a number of MIMO spatial streams supported, a numberof MIMO beam combinations to be trained, and MIMO training capabilityinformation.
 11. The method of claim 9, wherein the selected TX and RXsectors are determined based on signal to noise ratios (SNRs), andwherein the multiple best MIMO beam combinations are determined based onsignal to noise plus interference ratios (SNIRs), channel measurement,or channel measurement feedbacks.
 12. The method of claim 9, wherein oneTX/RX sector is beamformed from multiple TX/RX antennas or beamformers.13. The method of claim 9, wherein the training frames are received andprocessed simultaneously by multiple RX antennas.
 14. The method ofclaim 9, wherein the set of selected TX sectors is smaller or equal toall TX sectors, and wherein the set of selected RX sectors is smaller orequal to all RX sectors.
 15. The method of claim 9, wherein no more thanone TX sector of the best MIMO beam combinations is selected from thesame TX antenna or TX beamformer, and wherein no more than one RX sectorof the best MIMO beam combinations is selected from the same RX antennaor RX beamformer.
 16. A method comprising: (a) initiating a multipleinput and multiple output (MIMO) training procedure in a wirelessnetwork; (b) transmitting training packets using all TX sectors duringTX sector sweeping for obtaining a set of selected TX sectors for eachTX antenna, wherein each of the TX sectors corresponds to a specific TXantenna beam; (c) transmitting training packets using the selected TXsectors during RX sector sweeping for obtaining a set of selected RXsectors for each RX antenna corresponding to each selected TX sector,wherein each of the RX sectors corresponds to a specific RX antennabeam; and (d) obtaining multiple best MIMO beam combinations formultiple MIMO spatial streams based on channel measurement results,wherein each of the MIMO beam combinations includes one TX sector fromthe set of selected TX sectors and one RX sector from the set ofselected RX sectors.
 17. The method of claim 16, wherein the initiatingin (a) involves communicating a message that comprises at least one of anumber of TX/RX antennas, a number of TX/RX sectors for each TX/RXantenna, a number of MIMO spatial streams supported, a number of MIMObeam combinations to be trained, and MIMO training capabilityinformation.
 18. The method of claim 16, wherein the selected TX and RXsectors are determined based on signal to noise ratios (SNRs), andwherein the best beam combinations are determined based on signal tonoise plus interference ratios (SNIRs), channel measurement, or channelmeasurement feedbacks.
 19. The method of claim 16, wherein one TX/RXsector is beamformed from multiple TX/RX antennas or beamformers. 20.The method of claim 16, wherein the training packets are transmittedsimultaneously by multiple TX antennas.
 21. The method of claim 16,wherein the set of selected TX sectors is smaller or equal to all TXsectors, and wherein the set of selected RX sectors is smaller or equalto all RX sectors.
 22. The method of claim 16, wherein no more than oneTX sector of the best MIMO beam combinations is selected from the sameTX antenna or TX beamformer, and wherein no more than one RX sector ofthe best MIMO beam combinations is selected from the same RX antenna orRX beamformer.
 23. A method comprising: (a) initiating a multiple inputand multiple output (MIMO) training procedure in a wireless network; (b)receiving training packets using omni-direction antenna pattern duringTX sector sweeping for determining a set of selected TX sectors for eachTX antenna, wherein each of the TX sectors corresponds to a specific TXantenna beam; (c) receiving training packets using all RX sectors duringRX sector sweeping for determining a set of selected RX sectors for eachRX antenna corresponding to each selected TX sector, wherein each of theRX sectors corresponds to a specific RX antenna beam; and (d)determining multiple best MIMO beam combinations from the selected TXand RX sectors for multiple MIMO spatial streams based on channelmeasurement results, wherein each of the MIMO beam combinations includesone TX sector from the set of selected TX sectors and one RX sector fromthe set of selected RX sectors.
 24. The method of claim 23, wherein theinitiating in (a) involves communicating a message that comprises atleast one of a number of TX/RX antennas, a number of TX/RX sectors foreach TX/RX antenna, a number of MIMO spatial streams supported, a numberof MIMO beam combinations to be trained, and MIMO training capabilityinformation.
 25. The method of claim 23, wherein the selected TX and RXsectors are determined based on signal to noise ratios (SNRs), andwherein the beam combinations are determined based on signal to noiseplus interference ratios (SNIRs) channel measurement, or channelmeasurement feedbacks.
 26. The method of claim 23, wherein one TX/RXsector is beamformed from multiple TX/RX antennas or beamformers. 27.The method of claim 23, wherein the training packets are received andprocessed simultaneously by multiple RX antennas.
 28. The method ofclaim 23, wherein the set of selected TX sectors is smaller or equal toall TX sectors, and wherein the set of selected RX sectors is smaller orequal to all RX sectors.
 29. The method of claim 23, wherein no morethan one TX sector of the best MIMO beam combinations is selected fromthe same TX antenna or TX beamformer, and wherein no more than one RXsector of the best MIMO beam combinations is selected from the same RXantenna or RX beamformer.